Re: [PATCH] bpf: Use safer kvmalloc_array() where possible

[Yonghong Song <yhs@fb.com>]

On 5/26/22 3:24 AM, Dan Carpenter wrote:
> The kvmalloc_array() function is safer because it has a check for
> integer overflows.  These sizes come from the user and I was not
> able to see any bounds checking so an integer overflow seems like a
> realistic concern.
> 
> Fixes: 0dcac2725406 ("bpf: Add multi kprobe link")
> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> ---
>   kernel/trace/bpf_trace.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index 10b157a6d73e..7a13e6ac6327 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -2263,11 +2263,11 @@ static int copy_user_syms(struct user_syms *us, unsigned long __user *usyms, u32
>   	int err = -ENOMEM;
>   	unsigned int i;
>   
> -	syms = kvmalloc(cnt * sizeof(*syms), GFP_KERNEL);
> +	syms = kvmalloc_array(cnt, sizeof(*syms), GFP_KERNEL);
>   	if (!syms)
>   		goto error;
>   
> -	buf = kvmalloc(cnt * KSYM_NAME_LEN, GFP_KERNEL);
> +	buf = kvmalloc_array(cnt, KSYM_NAME_LEN, GFP_KERNEL);
>   	if (!buf)
>   		goto error;
>   
> @@ -2464,7 +2464,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr

For this part of change, there is a similar pending patch here:
https://lore.kernel.org/bpf/399e634781822329e856103cddba975f58f0498c.1652982525.git.esyr@redhat.com/
which waits for further review. That patch tries to detect the overflow
explicitly to avoid possible kernel dmesg warnings. (See function 
kvmalloc_node()).

>   		return -EINVAL;
>   
>   	size = cnt * sizeof(*addrs);
> -	addrs = kvmalloc(size, GFP_KERNEL);
> +	addrs = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
>   	if (!addrs)
>   		return -ENOMEM;
>   
> @@ -2489,7 +2489,7 @@ int bpf_kprobe_multi_link_attach(const union bpf_attr *attr, struct bpf_prog *pr
>   
>   	ucookies = u64_to_user_ptr(attr->link_create.kprobe_multi.cookies);
>   	if (ucookies) {
> -		cookies = kvmalloc(size, GFP_KERNEL);
> +		cookies = kvmalloc_array(cnt, sizeof(*addrs), GFP_KERNEL);
>   		if (!cookies) {
>   			err = -ENOMEM;
>   			goto error;